Circulating microRNAs and Response to Neoadjuvant Chemotherapy in Breast Cancer

This is a prospective, single-center observational study designed to evaluate circulating microRNA (miRNA) expression patterns in breast cancer patients receiving neoadjuvant chemotherapy (NAC). The primary aim is to examine changes in selected miRNAs (including miR-200 family members, miR-34a, miR-221/222, miR-155, and miR-146a) before NAC initiation and prior to surgery, and to determine their association with pathological response. Participants diagnosed with breast cancer and scheduled to receive standard NAC will be enrolled consecutively. Serum samples will be collected at two time points: (1) before NAC initiation, and (2) following completion of NAC but before surgery. Quantitative RT-PCR methods will be used to measure circulating miRNA expression levels. Pathological response will be evaluated using pathological complete response (pCR) status and Miller-Payne tumor regression grading. Secondary aims include examining the relationship between miRNA dynamics and breast cancer subtypes, evaluating the potential predictive value of miRNAs for NAC response, and assessing possible correlations between circulating tumor cell (CTC) levels and treatment outcomes. No investigational drugs or devices will be used in this study, and all treatments will follow standard clinical protocols. The study is expected to contribute to the identification of minimally invasive biomarkers that may support personalized treatment approaches and improve prediction of NAC response in breast cancer.